[dalke]

When I've arranged conferences, we had a certain number of time slots. It's a bit flexible, in that we can decide to allocate a longer time for two talks, or shorter time for three, depending on the talks.

It could be that they had a first pass at a schedule, used that to set a first cut for the reviewers, then adjusted the schedule once they figured they needed to add another 42 papers.

Also, not being accepted does not mean that a paper is poor. They used a rank system, so it only means that others had papers which appeared to be better.